1. Field of the Invention
The present invention relates to an optical sensing system, and more particularly, to an optical sensing system which uses two sensors to generate position signals.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a perspective view of a prior art optical sensing system 10. The optical sensing system 10 is frequently used in stepping motors for calculating rotation number of a stepping motor. The system 10 comprises a grid panel 12 and a sensing device 14 for detecting rotations of the grid panel 12. The grid panel 12 has a grid array 16 having a plurality of positioning holes 18 and an identification hole 20 installed around the periphery of the panel 12. The identification hole 20 is longer than other positioning holes 18. The sensing device 14 comprises three optical sensors 22, 24, and 26 installed at one side of the grid array 16 for detecting movements of the grid array 16 in left and right directions and generating corresponding sensing signals, and a light source (not shown) installed at another side of the grid array 16 for emitting light.
The two sensors 22 and 24 are arranged in a left-and-right pattern. When a positioning hole 18 of the grid array 16 passes through the sensing device 14 horizontally, the two sensors 22 and 24 will sequentially detect the light passed through the positioning hole 18 and sequentially generate corresponding sensing signals. Based on these sequentially generated sensing signals, the optical sensing system 10 can determine how many holes have been rotated and the direction of the rotation, and then generates displacement signals according to the sensing signals.
The sensor 26 is used for detecting the identification hole 20. Since the grid panel 12 has only one identification hole 20, whenever the identification hole 20 is detected by the sensor 26, the optical sensing system 10 will know the position of the grid panel 12. By using the sensor 26 to detect the position of the grid panel 12 and the sensors 22 and 24 to detect displacement of the grid panel 12, the optical sensing system 10 can generate position signals to represent the position of the grid panel 12 at each specific moment.
The major drawback of the optical sensing system 10 is that it uses three sensors to detect the position of the grid panel 12 since a three-sensor detector is quite expensive.